High-Pressure Processing Influences Antibiotic Resistance Gene Transfer in Listeria monocytogenes Isolated from Food...

The study aimed to assess the high-pressure processing (HPP) impact on antibiotic resistance gene transfer in L. monocytogenes from food and food processing environments, both in vitro (in microbiological medium) and in situ (in carrot juice), using the membrane filter method. Survival, recovery, and frequency of antibiotic resistance gene transfer analyses were performed by treating samples with HPP at different pressures (200 MPa and 400 MPa). The results showed that the higher pressure (400 MPa) had a significant effect on increasing the transfer frequency of genes such as fosX, encoding fosfomycin resistance, and tet_A1, tet_A3, tetC, responsible for tetracycline resistance, both in vitro and in situ. In contrast, the Lde gene (the gene encoding ciprofloxacin resistance) was not transferred under any conditions. In the food matrix (carrot juice), greater variability in results was observed, suggesting that food matrices may have a protective effect on bacteria and modify HPP efficacy. In general, an increase in MIC values for antibiotics was noted in transconjugants compared to donors. Genotypic analysis of transconjugants showed differences in genetic structure, especially after exposure to 400 MPa pressure, indicating genotypic changes induced by pressure stress. The study confirms the possibility of antibiotic resistance genes transfer in the food environment, even from strains showing initial susceptibility to antibiotics carrying so-called silent antibiotic resistance genes, highlighting the public health risk of the potential spread of antibiotic-resistant strains through the food chain. The findings suggest that high-pressure processing can increase and decrease the frequency of resistance gene transfer depending on the strain, antibiotic combination, and processing conditions.